In modern data processing or control systems, including telecommunications systems, a disk memory or its equivalent is used for storing information that is currently not being actively processed, but that can be fetched as needed to perform processing. Some of the information that is kept in disk memories is very valuable, in the sense that the loss associated with a loss of this memory is large. One example of this kind of information, is the billing records of a telecommunication system. If these billing records are lost, the revenue associated with the calls whose billing records have been accumulated in the disk is lost. Such loss can be in the tens and even hundreds of thousands of dollars in a large switching system. Accordingly, systems which use disk memory for such purposes require some form of back-up.
A common arrangement has two processors interconnected by a pair of SCSI buses, each SCSI (Small Computer System Interface) bus also passing through a disk platform for providing duplicate disk storage. A problem with this arrangement is that a failure of the SCSI bus may cause both processors to fail. Another problem is that if this arrangement is used to provide multiple copies of disk data, a heavy processing penalty is incurred in the main processors.
Another solution is to provide periodic back-up of the data in the disk by transmitting this data to some other processing system for storage on tape or other mass memory. Typically, this back-up procedure uses a great deal of processing time, and is therefore, performed only once a day during periods of very light load.
In view of the above, a problem of the prior art is that there is no really satisfactory arrangement for providing for ultra reliable storage of disk information in a simplex or a duplex processor system.
The above problem is solved and an advance is made over the prior art in accordance with this invention, wherein each processor has its own simplex or duplex disk memory and wherein, in addition, a separate disk platform comprising duplicate disk drives is connected to a simplex processor or to each processor of a duplex processor system, and wherein the duplicate disk drives are automatically updated to contain the same data as the disk of the processor system. Advantageously, such an arrangement provides a separate platform, having its own power rectification equipment for redundant disk memories which greatly enhances the reliability of the system. The system will only fail if either the disk platform fails and the active processor fails, or if both disk drives of the disk drive platform fail and one processor platform fails.
In accordance with one preferred implementation of Applicants"" invention, the presence of the disk platform is transparent to the individual processes running on each processor, so that information which is sent to the disk of a platform is automatically also sent to both disk drives of the disk platform. Advantageously, no additional processing time is required to update information in the disk platform.
In accordance with one preferred implementation of Applicants"" invention, duplex disk drives are provided on the disk platform. Advantageously, this greatly increases the reliability of the systems in which the weakest link is usually the disk drive.
In accordance with one feature of Applicants"" invention, when the disk drive(s) of a processor platform fail, the processor automatically uses the information stored in the disk drives of the disk drive platform. This operation is transparent to the individual processes running on the processor, since disk access software automatically steers a disk read or write request to a working disk drive whether that disk drive is part of the processor platform or a part of the disk drive platform.